This is a temporary work around for a bootloader that doesn't fit in the boot flash section of a particular device. For demonstration purposes, I want to put some of the overflow (which is not critical for self-programming) into the RWW section of flash, protecting it with software measures only. Although this is approach is not recommended in your FAQ, the demonstration would justify the move to new hardware with an appropriate boot flash section size.

OK. I'll bite again. Why would something as simple as a bootloader ever need FP? Sounds like you are making it over complicated.
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But, yes, doing it in the linker script rather than trying to use section-start 's looks like the best solution